Here’s why poisonous animals don’t poison themselves

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Toxic birds and frogs have evolved a way to avoid harm—but not in the way we thought.

In the forests of New Guinea lives a small, drab bird with a deadly secret. It’s called the hooded pitohui, and its orange and black feathers are laced with poison.

Simply touching the feathers of a pitohui is enough to make your hands feel like they’re on fire. But ingest a bit of the batrachotoxin, called BTX for short, and the poison stops your sodium channels from working, leading to paralysis and even death.

“You can think about these poisons as kind of a natural drug. It’s something that the animals use to protect themselves, because it… either gives a very unpleasant feeling to the thing that’s trying to eat them, or in the worst case, it kills the thing that’s trying to eat them,” says Daniel Minor, a biophysicist at University of California, San Francisco’s Cardiovascular Research Institute. (Learn the difference between a venomous and a poisonous animal.)

Scientists believe that the pitohui does not manufacture its own toxins, but rather acquires them from its tiny beetle prey. The same mechanism is suspected in poison dart frogs of Central and South America, which also carry BTX in their brightly colored skin.

All of which leads to an intriguing question—how do poisonous animals like the pitohui keep from poisoning themselves?

For decades, the best theory has been that the birds and frogs evolved specially adapted sodium channels—a part of the body that’s necessary for nerves, brain cells, and muscle cells to function properly—that are immune to BTX. After all, there are several examples of animals that shrug off toxins by this method, such as Egyptian mongooses that can survive cobra venom.

But a study published today in the Journal of General Physiology overturns that notion.

The researchers provide evidence that pitohui and poison frogs have what they call “toxin sponges,” or proteins that mop up the fatal toxins before they cause damage.